Many different myelographic contrast media have been employed for the radiographic visualization of the spinal cord. Unfortunately, none has fulfilled all the requirements of an ideal contrast medium-no toxicity, complete and rapid absorption, good radiographic contrast, and miscibility with the cerebrospinal fluid. Toxic reactions have been reported from the water soluble contrast media, which require the administration of a spinal anesthesia and have thus been employed clinically only in examination of the lumbosacral area. Some authors have advocated the use of new contrast media, Conray(Meglumine iothalamate), Dimer-X, for the lumbar myelography without a spinal anesthesia and obtained good results. The present work is an attempt to provoke and emphasize the toxicologic response and the pathologic changes by variation in amount of Conray and rate of injection. Each dog was prepared with a catheter in lumbar subarachnoid space under the light anest hesia. After recovery from the anesthesia, myelography was performed by lumbar subarachnoid injection of Conray by variations in amount of Conray and rate of injection under the control of a fluoroscope. The experimental conditions were varied as follows. 1. Conray was injected in variable amounts from the lumbosacral subarachnoid space to the high cervical and intracranial subarachnoid space. 2. Conray was injected in variable rate of injection. 3. Decadron was added to Conray in another group. 4. The brain and the spinal cord including the dura and the nerve roots were taken for the pathologic study in variable durations after myelography. The results were summarized as follows. 1. A large amount of Conray injection to the high cervical and intracranial subarachnoid space produced wevere toxic reactions followed by death. 2. Rapid injection of Conray was considered to elicit more toxic reactions. 3. The toxic reactions included changes in behavior and respiration, neck muscle spasms, paresis of forelegs and hindlegs, urination, defecation and epileptiform convulsions. 4. There was no difference in toxic reactions in adding Decardon. 5. Radiographic contrast densities were somewhat less than that of Pantopaque. Conray was freely miscible with the cerebrospinal fluid, thus providing total myeloraphy. 6. No recognizable reaction was noted in gross and histopathological examination.